The invention relates generally to antennas and, more particularly, to microstrip array antennas.
The number of direct satellite broadcast services has substantially increased worldwide and, as it has, the worldwide demand for antennas having the capacity for receiving such broadcast services has also increased. This increased demand has typically been met by reflector, or “dish,” antennas, which are well known in the art. Reflector antennas are commonly used in residential environments for receiving broadcast services, such as the transmission of television channel signals, from geostationary, or equatorial, satellites. Reflector antennas have several drawbacks, though. For example, they are bulky and relatively expensive for residential use. Furthermore, inherent in reflector antennas are feed spillover and aperture blockage by a feed assembly, which significantly reduces the aperture efficiency of a reflector antenna, typically resulting in an aperture efficiency of only about 55%.
An alternative antenna, such as a microstrip antenna, overcomes many of the disadvantages associated with reflector antennas. Microstrip antennas, for example, require less space, are simpler and less expensive to manufacture, and are more compatible than reflector antennas with printed-circuit technology. Microstrip array antennas, i.e., microstrip antennas having an array of microstrips, may be used with applications requiring high directivity. Microstrip array antennas, however, typically require a complex microstrip feed network which contributes significant feed loss to the overall antenna loss. Furthermore, many microstrip array antennas are limited to single polarization and to transmitting or receiving only a linearly polarized beam. Such a drawback is particularly significant in many parts of the world where broadcast services are provided using only circularly polarized beams. In such instances, the recipients of the services must resort to less efficient and more expensive, bulky reflector antennas, or microstrip array antennas which utilize a polarizer. A polarizer, however, introduces additional power loss to the antenna and produces a relatively poor quality radiation pattern. Moreover, when dual polarization is needed, two antennas of single polarization are required.
What is needed, then, is a low-cost, simple to manufacture and compact antenna having a high aperture efficiency, and which does not require a complex feed network, and which may be readily adapted for transmitting and/or receiving either linearly polarized or circularly polarized beams of single or dual polarization.